Drugs & Addiction

• Drugs and the brain

  • blood-brain barrier aids regulation of brains chemical enironment - selective semipermeable membrane that separates the bloodstream from the brain
  • molecules (e.g drugs) must be transported across barrier - to exert effects within brain
• Drug action

  • typically affect processes in synapses
  • agonists - facilitate post-synaptic effects
  • antagonists - inhibit post-synaptic effects
  • occurs in many ways
• Addiction

  • dugs = addctive because drug-taking behaviour reinforced
  • reinforcement (natural stimulus or drugs) linked to release of dopamine in nucleus accumbend - part of mesolimbic dopaminergic system
• addiction - positive reinforcement

  • presentation of appetitive stimulus in association with a behaviour
  • gives something - e.g. physical
• addiction - negative reinforcement

  removal of aversive stimulus in association with a behaviour
• addiction - temporal proximity 


  • of drug & behavior = important
  • heroin & morphine converted to dopamine in brain, but heroin = more addictive
  • Heroin crosses blood-brain barrier faster than morphine = more effective reinforcer
  • heroin = effects imidiate after behaviour = morphine relationship weaker
  • Animal self stimulation = better reinforcer than food, unless food is delivered immediately
• Learning changes brain = way perceive, perform, think, plan
• Learning - classical conditioning

  • Involves association between 2 stimuli & an automatic response
  • Unconditional Stimulus causes an Unconditional Response
  • If US paired with neutral stimulus - neutral stimulus can come to elicit, now conditioned, response
• Learning & the brain

  • Hebb’s Rule - synapse that is repeatedly active when postsynaptic neuron firing will become strengthened

  Classical conditioning

  • US (puff) → UR via strong synapse,
  • pairing tone with US strengthens weak synapse,
  • = tone becoming conditioned stimulus
• Hebbs rule - operant conditioning


  • Reinforcement system strengthens association between perception & behaviour
  • Basal ganglia integrates perception & action planning
  • Destruction leads to failure of instrumental conditioning